Methods and apparatuses for measuring the distance to a passive intermodulation source

Abstract

According to methods of performing measurements to determine a distance to a passive-intermodulation (“PIM”) source, a first RF signal comprising a first frequency and a second RF signal comprising a second frequency may be applied to a device under test. A reference signal comprising a higher-order intermodulation-product of the first frequency and the second frequency may also be generated. An output signal from the device under test and the reference signal may be digitized and a calibration measurement may be applied. A phase difference between the device under test output and the reference signal may be determined. A plurality of phase differences may be determined for multiple first frequencies, and from the plurality of phase differences, a delay may be calculated, which may be multiplied by the velocity of propagation on the medium connecting the device under test to the test equipment to determine a distance to the PIM source.

That which is claimed is: 
     
       1. A passive intermodulation (PIM) measurement apparatus, comprising:
 at least one signal generator that is configured to generate a first continuous wave radiofrequency (RF) signal having a first RF frequency and a second continuous wave RF signal having a second RF frequency; 
 a test apparatus configured to hold a device under test, the device under test configured to receive the first and second continuous wave RF signals from the at least one signal generator; 
 a first analog/digital converter configured to receive a reference signal comprising the first continuous wave RF signal and the second continuous wave RF signal and to digitize the reference signal, resulting in a digitized reference signal; 
 a second analog/digital converter configured to receive an output signal from the device under test and to digitize the output signal, resulting in a digitized output signal; and 
 a processor configured to calculate a distance to a source of passive intermodulation within the device under test, wherein the processor is configured to calculate the distance based on a phase difference calculated by the processor between the digitized reference signal and the digitized output signal. 
 
     
     
       2. The PIM measurement apparatus of  claim 1 , further comprising:
 a first image reject mixer configured to down-convert the reference signal prior to digitization of the reference signal by the first analog/digital converter; and 
 a second image reject mixer configured to down-convert the output signal prior to digitization of the output signal by the second analog/digital converter. 
 
     
     
       3. The PIM measurement apparatus of  claim 2 , further comprising a local oscillator common to both the first and second image reject mixers. 
     
     
       4. The PIM measurement apparatus of  claim 1 , wherein the processor is configured to calculate the phase difference using an arcsine function. 
     
     
       5. The PIM measurement apparatus of  claim 1 , wherein the processor is configured to calculate the phase difference using an arctangent function. 
     
     
       6. The PIM measurement apparatus of  claim 1 , wherein the processor is configured to calculate the phase difference using discrete Fourier transforms (DFTs) of the digitized reference signal and the digitized output signal. 
     
     
       7. The PIM measurement apparatus of  claim 1 , wherein the processor is coupled to a memory storing results of a calibration of the PIM measurement apparatus using a low-PIM termination, wherein the results of the calibration comprise a termination reference signal and a termination output signal. 
     
     
       8. The PIM measurement apparatus of  claim 1 , wherein the at least one signal generator comprises a first signal generator configured to generate the first continuous wave RF signal and a second signal generator configured to generate the second continuous wave RF signal. 
     
     
       9. The PIM measurement apparatus of  claim 8 , further comprising:
 a frequency-doubler configured to double the first RF frequency of the first continuous wave RF signal, resulting in a frequency-doubled first continuous wave RF signal; and 
 a mixer configured to mix the frequency-doubled first continuous wave RF signal and the second continuous wave RF signal, resulting in the reference signal. 
 
     
     
       10. The PIM measurement apparatus of  claim 8 , further comprising a combiner that couples a portion of the first continuous wave RF signal and the second continuous wave RF signal, resulting in the reference signal. 
     
     
       11. The PIM measurement apparatus of  claim 1 , wherein the device under test is a two-port device. 
     
     
       12. The PIM measurement apparatus of  claim 1 , wherein the device under test is a one-port device, and wherein the PIM measurement apparatus further comprises a diplexer or duplexer configured to separate a signal input to the device under test from a signal output by the device under test. 
     
     
       13. A passive intermodulation (PIM) measurement apparatus, comprising:
 at least one signal generator that is configured to generate a first continuous wave radiofrequency (RF) signal having a first RF frequency and a second continuous wave RF signal having a second RF frequency; 
 a test apparatus configured to hold a device under test, the device under test configured to receive the first and second continuous wave RF signals from the at least one signal generator; 
 a processor configured to receive an output signal from the device under test and a reference signal comprising a combination of the first continuous wave RF signal and the second continuous wave RF signal; and 
 a memory storing results of a calibration of the PIM measurement apparatus using a low-PIM termination, 
 wherein the processor is configured to calculate a distance to a source of passive intermodulation within the device under test based on the results of the calibration and based on a phase difference calculated by the processor between a digitized reference signal and a digitized output signal. 
 
     
     
       14. The PIM measurement apparatus of  claim 13 , further comprising:
 a first analog/digital converter configured to receive and digitize the reference signal, resulting in a digitized reference signal; and 
 a second analog/digital converter configured to receive and digitize the output signal from the device under test, resulting in a digitized output signal. 
 
     
     
       15. The PIM measurement apparatus of  claim 14 , further comprising:
 a first image reject mixer configured to down-convert the reference signal prior to digitization of the reference signal by the first analog/digital converter; and 
 a second image reject mixer configured to down-convert the output signal prior to digitization of the output signal by the second analog/digital converter. 
 
     
     
       16. A passive intermodulation (PIM) measurement apparatus, comprising:
 at least one signal generator that is configured to generate a plurality of first continuous wave radiofrequency (RF) signals each having an RF frequency within a frequency range, and a second continuous wave RF signal having a second RF frequency outside of the frequency range; 
 a combiner configured to receive each first continuous wave RF signal and the second continuous wave RF signal and output a reference signal comprising a combination thereof, resulting in a plurality of reference signals; 
 a test apparatus configured to hold a device under test, the device under test configured to receive each first continuous wave RF signal and the second continuous wave RF signal and output an output signal, resulting in a plurality of output signals; and 
 a processor configured to calculate a distance to a source of passive intermodulation within the device under test, wherein the processor is configured to calculate the distance based on phase differences calculated by the processor between respectively corresponding ones of the plurality of reference signals and the plurality of output signals. 
 
     
     
       17. The PIM measurement apparatus of  claim 16 , wherein the processor is configured to calculate the phase differences using an arcsine function. 
     
     
       18. The PIM measurement apparatus of  claim 16 , wherein the processor is configured to calculate the phase differences using an arctangent function. 
     
     
       19. The PIM measurement apparatus of  claim 16 , wherein the processor is configured to calculate the phase differences using discrete Fourier transforms (DFTs) of the reference signals and the output signals. 
     
     
       20. The PIM measurement apparatus of  claim 16 , wherein the processor is coupled to a memory storing results of a calibration of the PIM measurement apparatus using a low-PIM termination and wherein the processor is further configured to calculate the distance based on the results of the calibration.